Electric appliances, such as electric tools operated independently of the mains, for example, battery-operated screwdrivers, battery-operated drills or the like, can be driven by means of a plug-in, rechargeable battery pack which is connected by an electric switch to the electric motor of the tool.
An electric switch for use with a battery-operated electric tool is disclosed, for example, in U.S. Pat. No. 5,289,047. The switch has a housing on which, on the one hand, contacts in the form of contact clips are arranged for a pluggable electrical connection with mating contacts on the battery pack and on which, on the other hand, terminals are arranged for electrical connection to the electric motor. It has been found that damage can occur to the contact clips on the switch housing when the battery pack is being plugged into the electric tool.
It is an object of the invention to provide an improved electric appliance unit such as an electric tool, in which the contacts located in the tool housing are protected against damage when the battery pack is plugged in.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the electric appliance unit includes an appliance and a plug-in battery pack. The appliance has an appliance housing carrying an electric switch accommodated in a switch housing and including first electric contacts. The battery pack includes second electric contacts for engaging the first electric contacts. The battery pack has consecutive first and second positions upon introduction thereof into the appliance. In the first position the first and second electric contacts initially touch one another and in the second position the first and second electric contacts are in a final operative engagement. A first guiding arrangement guides and preliminarily centers the battery pack relative to the switch housing along a first insertion path extending to the first position to effect a coarse alignment of the first and second electric contacts upon reaching the first position. The first guiding arrangement includes a first guide component carried by the battery pack and cooperating, along the first insertion path, with a second guide component carried by the appliance housing. A second guiding arrangement guides and finely centers the battery pack relative to the switch housing along a second insertion path extending from the first position to the second position to effect a precise alignment of the first and second electric contacts with one another along the second insertion path. The second guiding arrangement includes a third guide component carried by the battery pack and cooperating, along the second insertion path, with a fourth guide component on the switch housing.
The guide components of the second guiding means on the switch housing and on the battery pack may be designed as projections (shoulders) which are at least as long as the associated contacts or mating contacts. The result is a reliable guidance when the battery pack is plugged in even before the contacts touch the mating contacts. The shoulders may have planar faces for the purpose of improving the guidance further. It is preferable to use a plurality of faces to form a shoulder, so that the shoulder on the battery pack is configured as a receptacle and the shoulder on the switch housing is designed as a plug-in guide. The plug-in guide can then be designed as an approximately cuboidal part closed at the side, or as an approximately U-shaped part partly open at the side.
As a rule, the switch housing is plastic and is produced as an injection-molded part. It is feasible to make one component of the second guiding means from the same material, integrally with the switch housing. In addition, a stop surface can be arranged between the components of the second guiding means on the battery pack and the switch housing, for example, for limiting the plug-in movement for protecting the contacts or for holding the switch in the tool housing. Furthermore, the component of the second centering and/or guiding means on the switch housing may be configured such that the battery pack can be introduced only in a specific position, thereby providing protection against polarity reversal of the battery pack. For this purpose, the component of the second guiding means on the switch housing may be provided with a slot or a key which engages in a corresponding counterpart of the component of the second guiding means on the battery pack.
It is a particular advantage of the invention that guidance of the battery pack is achieved when it is being plugged into the electric tool. This guidance effects a preliminary (coarse) centering of the battery pack until the electric contacts of the battery pack initially touch the electric contacts of the switch, and thereafter the guidance effects a subsequent fine centering for the final engagement of the electric contacts. As a result of this arrangement a tilting of the battery pack during its introduction into the tool is prevented. Protection against bending of the contacts when the battery pack is plugged in is thereby achieved, and thus the service life of the contacts is extended. Also, the contacts are subjected to less stress. Consequently, it is possible to use a less expensive material for the contacts, whereby cost advantages can be achieved. The shoulder (projection) on the switch housing also provides further protection for the contacts, thus preventing them from being bent during transport or assembly of the switch. This contributes to the reduction of waste.
Exemplary embodiments of the invention are shown in the drawings and will be described in more detail below.